The field of the present invention relates to the delivery of energy impulses (and/or fields) to bodily tissues for therapeutic purposes. It relates more specifically to the use of non-invasive methods and devices, particularly methods that make use of magnetic stimulation devices, to treat neurodegenerative disorders, using energy that is delivered by such devices. The medical disorders include Alzheimer's disease, Parkinson's disease, multiple sclerosis, postoperative cognitive dysfunction, and postoperative delirium. The treatment relates to stimulation of the vagus nerve to reduce neuro-inflammation, wherein pathways involving anti-inflammatory cytokines, the retinoic acid signaling system, and/or neurotrophic factors are enhanced, and/or pathways involving pro-inflammatory cytokines are inhibited.
Treatments for various infirmities sometime require the destruction of otherwise healthy tissue in order to produce a beneficial effect. Malfunctioning tissue is identified and then lesioned or otherwise compromised in order to produce a beneficial outcome, rather than attempting to repair the tissue to its normal functionality. A variety of techniques and mechanisms have been designed to produce focused lesions directly in target nerve tissue, but collateral damage is inevitable.
Other treatments for malfunctioning tissue can be medicinal in nature, but in many cases the patients become dependent upon artificially synthesized chemicals. In many cases, these medicinal approaches have side effects that are either unknown or quite significant. Unfortunately, the beneficial outcomes of surgery and medicines are often realized at the cost of function of other tissues, or risks of side effects.
The use of electrical stimulation for treatment of medical conditions has been well known in the art for nearly two thousand years. It has been recognized that electrical stimulation of the brain and/or the peripheral nervous system and/or direct stimulation of the malfunctioning tissue holds significant promise for the treatment of many ailments, because such stimulation is generally a wholly reversible and non-destructive treatment.
Nerve stimulation is thought to be accomplished directly or indirectly by depolarizing a nerve membrane, causing the discharge of an action potential; or by hyperpolarization of a nerve membrane, preventing the discharge of an action potential. Such stimulation may occur after electrical energy, or also other forms of energy, are transmitted to the vicinity of a nerve [F. RATTAY. The basic mechanism for the electrical stimulation of the nervous system. Neuroscience Vol. 89, No. 2, pp. 335-346, 1999; Thomas HEIMBURG and Andrew D. Jackson. On soliton propagation in biomembranes and nerves. PNAS vol. 102 (no. 28, Jul. 12, 2005): 9790-9795]. Nerve stimulation may be measured directly as an increase, decrease, or modulation of the activity of nerve fibers, or it may be inferred from the physiological effects that follow the transmission of energy to the nerve fibers.
Electrical stimulation of the brain with implanted electrodes has been approved for use in the treatment of various conditions, including movement disorders such as essential tremor and Parkinson's disease. The principle underlying these approaches involves disruption and modulation of hyperactive neuronal circuit transmission at specific sites in the brain. Unlike potentially dangerous lesioning procedures in which aberrant portions of the brain are physically destroyed, electrical stimulation is achieved by implanting electrodes at these sites. The electrodes are used first to sense aberrant electrical signals and then to send electrical pulses to locally disrupt pathological neuronal transmission, driving it back into the normal range of activity. These electrical stimulation procedures, while invasive, are generally conducted with the patient conscious and a participant in the surgery.
Brain stimulation, and deep brain stimulation in particular, is not without some drawbacks. The procedure requires penetrating the skull, and inserting an electrode into brain matter using a catheter-shaped lead, or the like. While monitoring the patient's condition (such as tremor activity, etc.), the position of the electrode is adjusted to achieve significant therapeutic potential. Next, adjustments are made to the electrical stimulus signals, such as frequency, periodicity, voltage, current, etc., again to achieve therapeutic results. The electrode is then permanently implanted, and wires are directed from the electrode to the site of a surgically implanted pacemaker. The pacemaker provides the electrical stimulus signals to the electrode to maintain the therapeutic effect. While the therapeutic results of deep brain stimulation are promising, there are significant complications that arise from the implantation procedure, including stroke induced by damage to surrounding tissues and the neuro-vasculature.
One of the most successful applications of modern understanding of the electrophysiological relationship between muscle and nerves is the cardiac pacemaker. Although origins of the cardiac pacemaker extend back into the 1800's, it was not until 1950 that the first practical, albeit external and bulky, pacemaker was developed. The first truly functional, wearable pacemaker appeared in 1957, and in 1960, the first fully implantable pacemaker was developed.
Around this time, it was also found that electrical leads could be connected to the heart through veins, which eliminated the need to open the chest cavity and attach the lead to the heart wall. In 1975 the introduction of the lithium-iodide battery prolonged the battery life of a pacemaker from a few months to more than a decade. The modern pacemaker can treat a variety of different signaling pathologies in the cardiac muscle, and can serve as a defibrillator as well (see U.S. Pat. No. 6,738,667 to DENO, et al., the disclosure of which is incorporated herein by reference).
Another application of electrical stimulation of nerves has been the treatment of radiating pain in the lower extremities by stimulating the sacral nerve roots at the bottom of the spinal cord (see U.S. Pat. No. 6,871,099 to WHITEHURST, et al., the disclosure of which is incorporated herein by reference).
Yet another application of electrical stimulation of nerves has been the treatment of epilepsy and depression by vagus nerve stimulation (VNS) [U.S. Pat. No. 4,702,254 entitled Neurocybernetic prosthesis, to ZABARA; U56341236 entitled Vagal nerve stimulation techniques for treatment of epileptic seizures, to OSORIO et al; US5299569 entitled Treatment of neuropsychiatric disorders by nerve stimulation, to WERNICKE et al]. For this procedure, the left vagus nerve is ordinarily stimulated at a location on the neck by first implanting an electrode there, then connecting the electrode to an electrical stimulator.
Despite the clinical success of VNS in treating epilepsy and depression, a specific mechanism underlying VNS relief of symptoms is not currently known. Vagus afferent fibers innervate several medullary structures; with the nucleus of the tractus solitarius (NTS) receiving bilateral inputs totaling approximately eighty percent of all vagal afferents. The NTS has widespread projections, including direct or multiple synaptic projections to the parabrachial nucleus, vermis, inferior cerebellar hemispheres, raphe nuclei, periaquaductal gray, locus coeruleus, thalamus, hypothalamus, amygdala, nucleus accumbens, anterior insula, infralimbic cortex, and lateral prefrontal cortex, making it difficult to determine the area or neuronal pathway mediating VNS effects. However, functional imaging studies have concluded that VNS may bring about changes in several areas of the brain, including the thalamus, cerebellum, orbitofrontal cortex, limbic system, hypothalamus, and medulla. The stimulation of particular areas of the brain has been suggested as a mechanism for the effects of VNS, but such localized stimulation of the brain may depend upon the parameters of the stimulation (current, frequency, pulse width, duty cycle, etc.). Those parameters may also determine which neurotransmitters are modulated (including norepinephrine, seratonin, and GABA) [Mark S. George, Ziad Nahas, Daryl E. Bohning, Qiwen Mu, F. Andrew Kozel, Jeffrey Borckhardt, Stewart Denslow. Mechanisms of action of vagus nerve stimulation (VNS). Clinical Neuroscience Research 4 (2004) 71-79; Jeong-Ho Chae, Ziad Nahas, Mikhail Lomarev, Stewart Denslow, Jeffrey P. Lorberbaum, Daryl E. Bohning, Mark S. George. A review of functional neuroimaging studies of vagus nerve stimulation (VNS). Journal of Psychiatric Research 37 (2003) 443-455; G. C. Albert, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain stimulation, vagal nerve stimulation and transcranial stimulation: An overview of stimulation parameters and neurotransmitter release. Neuroscience and Biobehavioral Reviews 33 (2009) 1042-1060; GROVES DA, Brown V J. Vagal nerve stimulation: a review of its applications and potential mechanisms that mediate its clinical effects. Neurosci Biobehav Rev (2005) 29:493-500; Reese TERRY, Jr. Vagus nerve stimulation: a proven therapy for treatment of epilepsy strives to improve efficacy and expand applications. Conf Proc IEEE Eng Med Biol Soc. 2009; 2009:4631-4].
To date, the selection of stimulation parameters for VNS has been highly empirical, in which the parameters are varied about some initially successful set of parameters, in an effort to find an improved set of parameters for each patient. A more efficient approach to selecting stimulation parameters might be to select a stimulation waveform that mimics electrical activity in the region of the brain that one is attempting to stimulate, in an effort to entrain the naturally occurring electrical waveform, as suggested in U.S. Pat. No. 6,234,953, entitled Electrotherapy device using low frequency magnetic pulses, to THOMAS et al. and application number US20090299435, entitled Systems and methods for enhancing or affecting neural stimulation efficiency and/or efficacy, to GLINER et al.
The present disclosure involves devices and medical procedures that stimulate nerves by transmitting energy to nerves and tissue non-invasively. A medical procedure is defined as being non-invasive when no break in the skin (or other surface of the body, such as a wound bed) is created through use of the method, and when there is no contact with an internal body cavity beyond a body orifice (e.g., beyond the mouth or beyond the external auditory meatus of the ear). Such non-invasive procedures are distinguished from invasive procedures (including minimally invasive procedures) in that invasive procedures do involve inserting a substance or device into or through the skin or into an internal body cavity beyond a body orifice.
Potential advantages of such non-invasive medical methods and devices relative to comparable invasive procedures are as follows. The patient may be more psychologically prepared to experience a procedure that is non-invasive and may therefore be more cooperative, resulting in a better outcome. Non-invasive procedures may avoid damage of biological tissues, such as that due to bleeding, infection, skin or internal organ injury, blood vessel injury, and vein or lung blood clotting. Non-invasive procedures are sometimes painless or only minimally painful and may be performed without the need for even local anesthesia. Less training may be required for use of non-invasive procedures by medical professionals. In view of the reduced risk ordinarily associated with non-invasive procedures, some such procedures may be suitable for use by the patient or family members at home or by first-responders at home or at a workplace, and the cost of non-invasive procedures may be reduced relative to comparable invasive procedures.
For example, transcutaneous electrical nerve stimulation (TENS) is non-invasive because it involves attaching electrodes to the surface of the skin (or using a form-fitting conductive garment) without breaking the skin. In contrast, percutaneous electrical stimulation of a nerve is minimally invasive because it involves the introduction of an electrode under the skin, via needle-puncture of the skin. Both TENS and percutaneous electrical stimulation can be to some extent unpleasant or painful, in the experience of patients that undergo such procedures. In the case of TENS, as the depth of penetration of the stimulus under the skin is increased, any pain will generally begin or increase.
Neurodegenerative diseases result from the deterioration of neurons, causing brain dysfunction. The diseases are loosely divided into two groups—conditions affecting memory that are ordinarily related to dementia and conditions causing problems with movements. The most widely known neurodegenerative diseases include Alzheimer (or Alzheimer's) disease and its precursor mild cognitive impairment (MCI), Parkinson's disease (including Parkinson's disease dementia), and multiple sclerosis.
Less well-known neurodegenerative diseases include adrenoleukodystrophy, AIDS dementia complex, Alexander disease, Alper's disease, amyotrophic lateral sclerosis (ALS), ataxia telangiectasia, Batten disease, bovine spongiform encephalopathy, Canavan disease, cerebral amyloid angiopathy, cerebellar ataxia, Cockayne syndrome, corticobasal degeneration, Creutzfeldt-Jakob disease, diffuse myelinoclastic sclerosis, fatal familial insomnia, Fazio-Londe disease, Friedreich's ataxia, frontotemporal dementia or lobar degeneration, hereditary spastic paraplegia, Huntington disease, Kennedy's disease, Krabbe disease, Lewy body dementia, Lyme disease, Machado-Joseph disease, motor neuron disease, Multiple systems atrophy, neuroacanthocytosis, Niemann-Pick disease, Pelizaeus-Merzbacher Disease, Pick's disease, primary lateral sclerosis including its juvenile form, progressive bulbar palsy, progressive supranuclear palsy, Refsum's disease including its infantile form, Sandhoff disease, Schilder's disease, spinal muscular atrophy, spinocerebellar ataxia, Steele-Richardson-Olszewski disease, subacute combined degeneration of the spinal cord, survival motor neuron spinal muscular atrophy, Tabes dorsalis, Tay-Sachs disease, toxic encephalopathy, transmissible spongiform encephalopathy, Vascular dementia, and X-linked spinal muscular atrophy, as well as idiopathic or cryptogenic diseases as follows: synucleinopathy, progranulinopathy, tauopathy, amyloid disease, prion disease, protein aggregation disease, and movement disorder. A more comprehensive listing may be found at the web site (www) of the National Institute of Neurological Disorders and Stroke (ninds) of the National Institutes of Health (nih) of the United States government (gov) in a subdirectory (/disorder/disorder_index) web page (htm). It is understood that such diseases often go by more than one name and that a nosology may oversimplify pathologies that occur in combination or that are not archetypical.
Certain other disorders, such as postoperative cognitive dysfunction have been described only recently, and they too may involve neuro-degeneration. Other disorders such as epilepsy may not be primarily neurodegenerative, but at some point in their progression they might involve nerve degeneration.
Despite the fact that at least some aspect of the pathology of each of the neurodegenerative diseases mentioned above is different from the other diseases, their pathologies ordinarily share other features, so that they may be considered as a group. Furthermore, aspects of their pathologies that they have in common often make it possible to treat them with similar therapeutic methods. Thus, many publications describe features that neurodegenerative diseases have in common [Dale E. Bredesen, Rammohan V. Rao and Patrick Mehlen. Cell death in the nervous system. Nature 443 (2006): 796-802; Christian Haass. Initiation and propagation of neurodegeneration. Nature Medicine 16(11, 2010): 1201-1204; Eng H Lo. Degeneration and repair in central nervous system disease. Nature Medicine 16(11, 2010):1205-1209; Daniel M. Skovronsky, Virginia M.-Y. Lee, and John Q. Trojanowski. Neurodegenerative Diseases: New Concepts of Pathogenesis and Their Therapeutic Implications. Annu. Rev. Pathol. Mech. Dis. 1 (2006): 151-70; Michael T. Lin and M. Flint Beal. Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases. Nature 443 (2006): 787-795; Jorge J. Palop, Jeannie Chin and Lennart Mucke. A network dysfunction perspective on neurodegenerative diseases. Nature 443 (2006): 768-773; David C. Rubinsztein. The roles of intracellular protein-degradation pathways in neurodegeneration. Nature 443 (2006): 780-786].
One such common feature is the presence of inflammation, wherein the body recognizes the abnormality of the relevant neuronal tissue and responds to minimize or repair the effects of the abnormality and/or eventually destroy the abnormal tissue. [Sandra Amor, Fabiola Puentes, David Baker and Paul van der Valk. Inflammation in neurodegenerative diseases. Immunology, 129 (2010), 154-169; Mark H. DeLegge. Neurodegeneration and Inflammation. Nutrition in Clinical Practice 23 (2008):35-41; Tamy C Frank-Cannon, Laura T Alto, Fiona E McAlpine and Malù G Tansey. Does neuroinflammation fan the flame in neurodegenerative diseases? Molecular Neurodegeneration 2009, 4:47-59; Christopher K. Glass, Kaoru Saijo, Beate Winner, Maria Carolina Marchetto, and Fred H. Gage. Mechanisms Underlying Inflammation in Neurodegeneration. Cell 140 (2010): 918-934; V. Hugh Perry. The influence of systemic inflammation on inflammation in the brain: implications for chronic neurodegenerative disease. Brain, Behavior, and Immunity 18 (2004): 407-413; Marianne Schultzberg, Catharina Lindberg, Åsa Forslin Aronsson, Erik Hjorth, Stefan D. Spulber, Mircea Oprica. Inflammation in the nervous system—Physiological and pathophysiological aspects. Physiology & Behavior 92 (2007) 121-128; Frauke Zipp and Orhan Aktas. The brain as a target of inflammation: common pathways link inflammatory and neurodegenerative diseases. Trends in Neurosciences 29 (9, 2006) 518-527]. It is understood that inflammation may accompany not only neurodegenerative disease, but also brain injury that is caused, for example, by trauma, stroke, or infection. Consequently, the methods that are disclosed herein may also be applicable to any situation in which inflammation in the central nervous system presents a danger to the patient.
Because excessive and prolonged inflammation may destroy nervous tissue that is associated with neurodegenerative diseases, therapies have been proposed to prevent, reduce, or eliminate the immune response in such inflammation, or to repair damage that may have been produced by inflammation. Inflammation is modulated by cytokines, which are small cell-signaling protein or peptide molecules that are secreted by glial cells of the nervous system, by numerous cells of the immune system, and by many other cell types. Some cytokines may regarded as hormones, but in what follows, the term cytokine is used to refer to any of those immuno-modulating molecules, with the understanding that they may also participate in pathways other than immunomodulation.
In general, one may adopt two approaches to reduce or prevent inflammation that is modulated by cytokines. First, one may attempt to inhibit the release or effectiveness of cytokines that promote inflammation. Those cytokines are called pro-inflammatory, and the first approach is essentially an anti-pro-inflammatory strategy. Because pro-inflammatory cytokines may promote the release of other pro-inflammatory cytokines, the goal is especially to inhibit the release of the initially released pro-inflammatory cytokines in an inflammatory cascade. For example, the cytokine tumor necrosis factor (TNF-alpha) is considered to be a pro-inflammatory cytokine of central importance, and anti-TNF-alpha strategies seek to inhibit the release or effectiveness of TNF-alpha that is released from immune and other cells [Ian A. Clark, Lisa M. Alleva, Bryce Vissel. The roles of TNF in brain dysfunction and disease. Pharmacology & Therapeutics 128 (2010): 519-548; Melissa K McCoy and Malú G Tansey. TNF signaling inhibition in the CNS: implications for normal brain function and neurodegenerative disease. Journal of Neuroinflammation 2008, 5:45].
A second approach to reducing inflammation that is modulated by cytokines is to enhance and/or stimulate the release or effectiveness of cytokines that inhibit inflammation. Those cytokines are called anti-inflammatory, and the second approach is essentially a pro-anti-inflammatory strategy. As indicated below, pro-anti-inflammatory mechanisms are often associated with the repair of tissue, which may correspond in the adult to mechanisms that were used in the embryo to create tissue originally. The cytokine transforming growth factor beta (TGF-beta) is often regarded as anti-inflammatory, but as described presently, its anti-inflammatory capabilities are contingent upon certain conditions being met. According to the second approach, one endeavors to promote such conditions, as well as to promote the release of, for example, TGF-beta into a potentially inflammatory environment.
In a series of publications, patents, and patent applications, Kevin J. TRACEY and colleagues described electrical stimulation of the vagus nerve in an attempt to effect the first, anti-pro-inflammatory strategy [Kevin J. Tracey. The inflammatory reflex. Nature 420 (2002): 853-859; Kevin J. Tracey. Physiology and immunology of the cholinergic anti-inflammatory pathway. J. Clin. Invest. 117 (2007): 289-296; Kevin J. Tracey. Understanding immunity requires more than immunology. Nature Immunology 11 (2010): 561-564; G. R. Johnston and N. R. Webster. Cytokines and the immunomodulatory function of the vagus nerve. British Journal of Anaesthesia 102(4, 2009): 453-462]. U.S. Pat. No. 6,610,713 and U.S. Pat. No. 6,838,471, entitled Inhibition of inflammatory cytokine production by cholinergic agonists and vagus nerve stimulation, to TRACEY, mention treatment of neurodegenerative diseases within a long list of diseases, in connection with the treatment of inflammation through stimulation of the vagus nerve. According to those patents, “Inflammation and other deleterious conditions . . . are often induced by proinflammatory cytokines, such as tumor necrosis factor (TNF; also known as TNF.alpha. or cachectin) . . . ” The patents go on to state that “Proinflammatory cytokines are to be distinguished from anti-inflammatory cytokines, . . . , which are not mediators of inflammation.” It is clear from those patents that the objective of TRACEY and colleagues is only to suppress the release of proinflammatory cytokines, such as TNF-alpha. There is no mention or suggestion that the method is intended to modulate the activity of anti-inflammatory cytokines, and in fact, the text quoted above disclaims a role for anti-inflammatory cytokines as mediators of inflammation. Those patents and applications make a generally unjustified dichotomy between pro- and anti-inflammatory cytokines, by suggesting that a cytokine could be one or the other, but not both. In particular, the patents make no mention of the cytokine TGF-beta, and there is no suggestion that the role of a cytokine in regards to its pro- or anti-inflammation competence may be inherently indeterminate or indefinite unless more information is provided about the presumed physiological environment in which the cytokine finds itself.
Treatment of neurodegenerative diseases is also mentioned within long lists of diseases in the following related applications to TRACEY and his colleague HUSTON, wherein stimulation of the vagus nerve is intended to suppress the release of proinflammatory cytokines such as TNF-alpha: US20060178703, entitled Treating inflammatory disorders by electrical vagus nerve stimulation, to HUSTON et al.; US20050125044, entitled Inhibition of inflammatory cytokine production by cholinergic agonists and vagus nerve stimulation, to TRACEY; US20080249439, entitled Treatment of inflammation by non-invasive stimulation to TRACEY et al.; US20090143831, entitled Treating inflammatory disorders by stimulation of the cholinergic anti-inflammatory pathway, to HUSTON et al; US 20090248097, entitled Inhibition of inflammatory cytokine production by cholinergic agonists and vagus nerve stimulation, to TRACEY et al. The same observations made above in connection with U.S. Pat. No. 6,610,713 and U.S. Pat. No. 6,838,471 apply to those applications as well.